1. Field of the Invention
The present invention relates to magnetic disk drives and, more specifically, to signal processing circuits for magneto-resistive (MR) heads.
2. Description of the Related Art
The principle of operation of MR heads is based on the ability of metals to change their resistance in the presence of a magnetic field. A typical MR head has an MR element composed of a thin film (e.g., about 250 nm in thickness) of Ni—Fe alloy, also called permalloy, which converts magnetic field variations at the surface of a magnetic storage medium (e.g., a magnetic platter) into resistance variations. The resistance variations are then converted into a differential voltage swing at the output of the MR head.
MR technology solves numerous problems associated with magneto-inductive heads, such as the dependence of signal amplitude on the rotational speed of the magnetic disk. However, MR heads have created new challenges for disk drive designers. One problem is the asymmetry in the response of a biased MR element to magnetic flux changes of opposite polarity. As a result, positive and negative pulses in the output signal of the MR head have different amplitudes, which impairs both servo and read channel performance in the disk drive.